Or if you are hiding like...a joint, or anything small as a cig, just take the tobacco out of the cig, slide the j in the cig, and a cig in a pack has the filter up, so uhh yea they would see a filter and not a j.
DONT THINK THATS HOW YOU CAN GET AWAY WITH THINGS AT SCHOOL. At school if you get caught with something (e.g. a pack of cigs) in most states they are required to take every cig out and break it.